1. Field of the Invention
Embodiments of the present invention generally relate to testing systems for electronic devices on substrates. In addition, embodiments of the present invention generally relate to an improved prober for conducting a thin film transistor liquid crystal display array test on a variety of flat panel substrate designs.
2. Description of the Related Art
Active matrix liquid crystal displays (LCDs) are commonly used for applications such as computer and television monitors, cell phone displays, personal digital assistants (PDAs), and an increasing number of other devices. Generally, an active matrix LCD comprises two glass plates having a layer of liquid crystal materials sandwiched therebetween. One of the glass plates typically includes a conductive film disposed thereon. The other glass plate typically includes an array of thin film transistors (TFTs) coupled to an electrical power source. Each TFT may be switched on or off to generate an electrical field between a TFT and the conductive film. The electrical field changes the orientation of the liquid crystal material, creating a pattern on the LCD.
In order to provide quality control for thin film transistors on a large area glass substrate, it is desirable to conduct a liquid crystal display “array test.” The array test allows a TFT LCD manufacturer to monitor and correct defects in the pixels during processing. A known method of testing pixels is known as electron beam testing, or “EBT.” During testing, each TFT is positioned under an electron beam. This is accomplished by positioning a substrate on a table positioned below the beam, and moving the table in “x” and “y” directions to sequentially position each TFT on the substrate below the electron beam test device. One such device which enables flat panel display fabricators to test devices formed on flat panels is a PUMA™ electron beam tester available from AKT, Inc., a subsidiary of Applied Materials, Inc. located in Santa Clara, Calif.
In order for the LCD array test to be conducted, a “prober” is used. A typical prober consists of a frame that usually covers the entire substrate under investigation. The frame has a plurality of electrical contact pins thereon at locations that match the contact pads of the substrate. Electrical connection to the pins is accomplished by fine wire connections to an electronics driver board. The board is usually software controlled.
In operation, the substrate is raised into contact with the prober. More specifically, the contact pads of the substrate are placed into contact with the electrical pins of the prober. The contact pads, in turn, are in electrical communication with a pre-defined set of the thin film transistors, or “pixels.” An electrical current is delivered through the pins and to the contact pads. The current travels to and electrically excites the corresponding pixels. An electron beam senses voltages in the excited pixels in order to confirm operability of the various thin film transistors on the substrate.
In the past, each prober has been custom made for a particular display layout design. This means that each electrical device and substrate layout has required a different prober frame having the matching configuration for the device array. The result is that the purchaser of semiconductor fabrication machinery must also purchase a uniquely compatible prober in order to test the fabricated pixels.
Modification of an individual prober for a new device layout is expensive. Therefore, it is desirable to provide a prober that is configurable to match a different substrate sizes and different device layouts. It is also desirable to provide a prober that can be functionally adjusted for different display layouts or arrangements.